Abstract
The following new OBN and OBC stars have been found: HD 75860, BC 2 Iab; HD 104565, OC 9.7 Ia; HD 123008, ON 9.7 Iab; and HD 150574, ON 9 III(n). Examples of morphologically more moderate CNO anomalies in OB spectra are also discussed; it is concluded that the O9-B0 7 supergiants of the Orion Belt and NGC 6231 (the nuclear cluster of Scorpius OB1) are systematically nitrogen-deficient. One possible explanation of these nitrogen-deficient supergiants in sub-associations is that they may have formed from nitrogen-deficient clouds; another could be that the more numerous morphologically normal supergiants show the effects of mixing in their spectra, while the nitrogen-deficient ones are relatively younger or have not yet been red supergiants. No red supergiants are found in Sco OB1, whereas NGC 3293 contains two B0 supergiants with normal CNO spectra together with a red supergiant. The paper will appear in the Astrophysical Journal, April 15, 1976.
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